This invention relates to slow-release pesticide generators. More particularly, this invention relates to slow-release pesticide generators comprising a non-volatile vinyl phosphate pesticide dispersed in a plasticized thermoplastic resin wherein the pesticide migrates onto the resin surface and is maintained thereon in a certain crystalline form. These generators are useful in the control of non-vertebrate pests and particularly in the control of ectoparasites such as fleas and ticks on warm-blooded animals.